Frequently Asked Questions about Electricity

Why did the U.S.A. choose 120v for household current and Europe choose 220v?

It appears that the 120 was chosen somewhat arbitrarily. Edison came up with a high-resistance lamp filament he thought desirable to keep distribution losses down. In 1882, he applied for patents on a 3-wire system which gave 220v transmission with 110v lamps.

Why does US use 60 cycles and Europe use 50 cycles?

Many frequencies were used in the 19th Century for various applications, with the most prevalent being the 60 c/s supplied by Westinghouse-designed central stations for incandescent lamps. The development of a synchronous converter which operated best at 60 cycles encouraged convergence toward that standard. Around 1900, the introduction of the high-speed turbine led to settlement on two standards: 25 cycles for transmission and for large motors (this had been a compromise decision at Niagara Falls), and 60 cycles for general purpose systems. Meanwhile, in Germany, AEG -- which used 50 cycles -- had a virtual monopoly, and this standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and Britain only settled on the 50 cycle standard after World War II.

The first test signals were sent on 5 August, 1858, between Trinity Bay, Newfoundland and Valentia, Ireland. It took some time to adjust the instruments however, and it wasn´t until 16 August that Queen Victoria and President Buchanan exchanged messages. First commercial message - from Cunard agents in New York to report the collision of the steamships "Arabia" and "Europa" - was transmitted on 20 August. The cable´s insulation degraded quickly, and its messages became unintelligible on the first of September, one month after it was laid. On 27 July, 1866 the first permanent transatlantic link was completed.

When was the first transatlantic radio transmission?

How did the convention that electric current flows from positive to negative get established?

In the 18th century a number of people made investigations of static electricity. Charles Dufay distinguished between vitreous electricity (the sort created when glass or rock crystal was rubbed) and resinous electricity (the sort created when resin or a wax rod was rubbed). Dufay proposed a two-fluid theory of electricity, the two fluids corresponding to the two types of electricity. Benjamin Franklin proposed a one-fluid theory, hypothesizing that the two apparent types of electricity were, in fact, occurrences of excesses and deficiencies of a single electrical fluid. Franklin introduced the terminology 'positive' and 'negative' to denote, respectively, an excess of electrical fluid and a deficiency of electrical fluid. It was on the basis of certain charging and discharging phenomena that Franklin assigned the designations 'positive' and 'negative', and in the 19th century the terminals of electric batteries were labeled 'plus' and 'minus'. Early in the 20th century it became clear that in most instances of the transfer of electric charge, it is electrons (negative charge carriers) that move, but by that time the labeling conventions had been firmly established.